Wireless network system, relay terminal and program

ABSTRACT

A wireless network system relays a broadcast signal in multiple stages and distributes data to terminals there around, and relay terminals determine whether to relay broadcast packets according to the direction vector and the position information, specified by the information transmission source terminal, referring to their own position information and direction, and relay and accept the packets or ignore them.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the field of wireless network systems, andrelay terminals and programs in the wireless network systems, in whichan information transmission source terminal broadcasts data, and inwhich relay terminals relay in multiple stages and distribute data toperipheral terminal devices.

Priority is claimed on Japanese Patent Application No. 2004-55227, filedFeb. 27, 2004, the content of which is incorporated herein by reference.

2. Description of Related Art

In the wireless network system, a technique called “flooding” is appliedto notify receipt of broadcasted packets. “Flooding” is a technique todistribute data to terminals distributed around an informationtransmission source terminal. The information transmission sourceterminal transfers (broadcasts) the broadcast packet and all theterminals that receive it broadcast it. The process is repeated. Inother words, when processing a flooding, data is transferred toterminals located in all the directions.

On the other hand, for the purpose of reducing the number of terminalequipment to relay, “the information transmission method, theinformation transmission system, the information terminal, and theinformation memory medium” (for example, in Japanese Patent Application,Unexamined Publication No. 2001-339399) have been proposed. In thisproposal, terminals relay the data only when the current informationdirection vector and the current direction vector show the samedirection. The current information direction vector shows the movementof the data from the information transmission source terminal to thereply terminal. The current direction vector shows the movementdirection of the relay terminal. However, the method transfers the datain all the directions.

In some cases, the data can be effective only for the terminals in somedirections and some positions. In this case, the data cannot be usefulin other directions and other positions. Transferring such data to alldirections wastes electric power and resources for wireless terminals.

For example, in the case of a multi-hop radio network, formed amongcars, informs about the approach of the emergency vehicle. Informationhas importance for cars in the area where an emergency vehicle will passby shortly. With the conventional technique, notifying information inall directions, wireless terminals, behind the emergency vehicle, mightwaste resources. Also, in notification of traffic accident information,the information is meaningful for cars which head for the place wherethe accident occurred. That is why, for example, on a one-way road, itcan also be a waste of the wireless terminal resources.

SUMMARY OF THE INVENTION

In view of the above-mentioned circumstances, the invention aims tooffer the relay terminal and the program in the wireless network systemwhich achieves effective use of the resource of the wireless terminal.The system in this invention, referring to the position information andthe direction vector, given by the information transmission sourceterminal, distinguishes whether or not to relay the received broadcastpacket.

According to the first aspect of the invention, a wireless networksystem relaying a broadcast signal in multiple stages and distributesdata to terminals there around, comprises: a transmission sourceterminal which generates the broadcast-signal; and multiple relayterminals which determine whether it is necessary to relay a broadcastpacket according to a direction vector and a position informationspecified by the information transmission source terminal referring tothe position information and its own direction.

According to the second aspect of the invention, a relay terminal in awireless network system which relays a broadcast-signal in multiplestages and distributes data to terminals there around, comprises: apacket receiving part which receives a broadcast packet from aninformation transmission source terminal; a self-position informationacquisition part which determines its own position; and a relay judgingpart which determines whether it is necessary to relay the broadcastpacket according to a direction vector and position information in thebroadcast packet, specified by the information transmission sourceterminal.

According to the third aspect of the invention, in the above-mentionedrelay terminal, the relay judging part determines whether to relay thebroadcast packet according to an available angle range specified by theinformation transmission source terminal in the broadcast packet.

According to the fourth aspect of the invention, in the above-mentionedrelay terminal, the relay judging part determines whether to relay thebroadcast packet according to relay position range in the broadcastpacket, specified by the information transmission source terminal.

According to the fifth aspect of the invention, the above-mentionedrelay terminal further provides an acceptance judging part whichdetermines whether to accept the broadcasted packet according to a dataavailable range in the broadcast packet, specified by the informationtransmission source terminal.

According to the fifth aspect of the invention, a program for a relayterminal in a wireless network system which relays a broadcast signal inmultiple stages and distributes data to terminals there around,comprises: a packet receiving process which receives a broadcast packetfrom a transmission source; a self-position information acquisitionprocess which obtains position of the relay terminal; and a relayjudging process which determines whether to relay the broadcast packetaccording to a direction vector in the broadcast packet, specified bythe information transmission source terminal, and position information.

The system in this invention, referring to the position information andthe direction vector, given by the information transmission source,distinguishes whether or not to relay the received broadcast packet.This helps to reduce the amount of unnecessary data relay and terminalsaccept the data only when it is required. This invention thereforeachieves effective use of wireless terminal resources. Also, terminalscan prevent transmission of packets which are useless and save theelectric power.

This invention is effective for an information distribution in thenetwork with ad hock data transmission such as information ofapproaching emergency vehicles or accident information, especially inITSs (Intelligent Transport Systems).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the process sequence of the wireless network system in thisinvention.

FIG. 2 shows a block diagram which shows the internal design of therelay terminal from the functional point of view in this invention.

FIG. 3 shows a flow chart of the process in relay terminal.

FIG. 4 shows another flow chart of the process in relay terminal.

FIG. 5 describes positions between the car and the emergency vehicle.

FIG. 6 is the image figure of the car and the emergency vehicle.

FIG. 7 is the image figure of the accident car and the emergencyvehicle.

FIG. 8 describes the position of the accident car and the emergencyvehicle in another implementation form of this invention.

FIG. 9 describes the position of the accident car and the emergencyvehicle.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a process sequence of the wireless network system in thisinvention. In FIG. 1, the relationship between a broadcasting terminalas information transmission source 1 and relay terminals 2 to n (n is aninteger, larger than or equal to 2) are shown.

In FIG. 1, information transmission source 1 adds a parameters about itsown “position information”, “direction”, “position offset”, “relayterminal position range”, “data available position range”, and“available angle range” to the broadcast packet and transmits it (S1).The “position offset” is an offset for shifting a reference positionfrom an actual position of information transmission source 1 to the reardirection with respect to the direction of the movement. The “relayterminal position range” is a distance from information transmissionsource 1 for determining whether the relay terminals 2-n perform relay.When the distance is smaller than the “relay terminal position range”,relay terminal 2-n relay the data from information transmission source 1to other relay terminals. The “data available position range” is adistance from information transmission source 1 for determining whetherthe relay terminals 2-n notify information to an application program.When the distance from the source 1 to relay terminal 2-n is smallerthan the threshold, relay terminal 2-n notifies the existence of theinformation transmission source 1 to the appropriate applicationprogram.

The relay terminal 2 receives the broadcast packet from informationtransmission source 1, and calculates the position vector, starting frominformation transmission source 1 as the reference, referring to its ownposition information. Moreover, the position vector is calculated basedon the position that is shifted only for the position offset from theposition information of information transmission source 1, to thereverse direction of the direction of the movement of informationtransmission source 1.

Also, relay terminal 2 takes data from information transmission source 1as a candidate to relay and accept data when cosine θ obtained from theinner product of the “direction” vector and position vector is largerthan the value obtained from “available angle range”. For example, when“available angle range” is 90 degrees and when cosine θ is larger than0, data from information transmission source 1 can be a candidate. Whendata from information transmission source 1 is a candidate, relayterminal 2 calculates the size of the position vector. Also, relayterminal 2 relay from information transmission source 1 when the size ofthe position vector is smaller than the “relay terminal position range”.Also, relay terminal 2 accepts the data from information transmissionsource 1 when the size of position vector is smaller than the “dataavailable position range”. FIG. 5 shows “data available position range”or “relay terminal position range” with hatching, including therelationship between a vehicle and approaching emergency vehicle asmentioned above.

FIG. 2 is the block diagram which shows internal design of relayterminal in one implementation of this invention.

Relay terminal 2 judges whether or not the received broadcast packetsshould be relayed according to the position and direction vector ofitself, based on the direction vector and position information specifiedby information transmission source 1. The relay terminal 2 is comprisedof packet receiving part 21, self-position information acquisition part22, vector calculation part 23, relay judging part 24, acceptancejudging part 25, data transmitting part 26, and application executionpart 27.

Packet receiving part 21 receives the broadcasted packet frominformation transmission source 1 and supplies it to vector calculationpart 23, relay judging part 24 and acceptance judging part 25.Self-position information acquisition part 22 calculates its ownposition information and supplies the information to vector calculationpart 23, using, for example a GPS (Global Positioning System) receiver.

Vector calculation part 23 performs a vector operation referring to thedirection vector and the position information which are specified by thetransmission source terminal, and to the position information anddirection vector of relay terminal 2, and supplies the operation resultsto relay judging part 24 and acceptance judging part 25. Relay judgingpart 24 determines whether or not the relay of received broadcastpackets is required, based on the vector value output from the vectorcalculation part 23 and on “relay terminal position range”. Acceptancejudging part 25 determines whether or not packets received by packetreceiving part 21 should be accepted, based on the vector value outputfrom vector calculation part 23, “data available position range”,referring to “data available position range” contained in thebroadcasted packets received by packet receiving part 23.

The determination results are transmitted to data transmitting part 26and application execution part 27, so that data is transmitted orapplication programs are executed.

FIG. 6 is a figure to explain one implementation of this invention. Thisis a drawing of approaching emergency vehicle. Hereinafter, explanationof this implementation form applies concrete examples such as thenotation of approaching emergency vehicle. FIG. 3 shows the flow chartof the process.

In FIG. 3, the emergency vehicle is information transmission source 1.Relay terminal 2 receives a broadcasted packet from the emergencyvehicle via packet receiving part 21 (S21) and calculates the positionvector, based on the position of information transmission source 1, fromvector calculation part 23 (S22) with reference to the positioninformation of its own. Here, the position vector is based on theposition that is shifted only for the position offset from the positioninformation of information transmission source 1, to the reversedirection of the direction of the movement of information transmissionsource 1.

Vector calculation part 23 calculates cosine θ from the inner product ofthe above-mentioned position vector and notified movement directionvector (S23). When the packet from information transmission source 1 istaken as a candidate to relay and to accept when cosine θ (S23),calculated from the inner product of the direction vector and positionvector, is larger than the cosine of the “available angle range”.

For example, when the “available angle range” is 90 degrees and whencosine θ is larger than 0 (S24, cosine θ>α), vector calculation part 23takes the packet from information transmission source 1 as a candidateand supplies it.

When the packet from information transmission source 1 is a candidate,relay judging part 24 calculates the size of position vector. Also,relay judging part 24 relay the packet from information transmissionsource 1 when the size of position vector is smaller than “relayterminal position range” (S25, S26). Also, relay judging part 24 decidesto ignore the data from information transmission source 1 when the sizeof position vector is larger than “relay terminal position range” (S25,S29). Acceptance judging part 25 compares the size of position vector,calculated by relay judging part 24, to “data available position range”(S27). When the size of the position vector is smaller than the “dataavailable position range”, application execution part 27 decides toaccept data from information transmission source 1(S28) and executes anappropriate program.

Details are explained below.

First, the emergency vehicle, which is information transmission source1, transmits the broadcasted packet including its own “positioninformation”, “traveling direction”, “position offset”, “relay terminalposition range”, “data available position range”, and “available angle(90 degrees)”. Hereafter, the broadcasted packet is called anotification packet for approaching emergency vehicle.

The car (relay terminal 2), which received the notification packet forapproaching emergency vehicle, calculates the position vector, startingfrom information transmission source 1, referring to its own positioninformation.

Next, relay terminal 2 calculates cosine θ from the inner product of thedirection vector, transmitted from information transmission source 1,and the position vector, calculated above. Also, relay terminal 2compares cosine θ and the notification packet for approaching emergencyvehicles. That is, relay terminal 2 relays the packet when the distancefrom relay terminal 2, providing in the car, to information transmissionsource 1, providing in the emergency vehicle, is less than “relayterminal position range” and moreover, when the position vector “fromthe emergency vehicle position to the car position” and directionvector, transmitted from information transmission source 1, have samedirection in the range of ±90′ (calculated inner product is positive).

In this case, the vector, from the emergency vehicle to the car, startsfrom the position of the emergency vehicle, but is shifted for positionoffset (for example, about 20 meters to the back of the emergencyvehicle). In other words, relay terminal 2 should stop the relay wheninformation transmission source 1, the emergency vehicle, passes by alittle.

Similarly, relay terminal 2 receives packets and outputs them to theapplication, when the distance between the car and the emergency vehicleis less than the “data available position range”, and moreover, when thevector, from a position of the emergency vehicle to the position of thecar, and the direction vector, received from information transmissionsource 1, are in the same direction (an inner product is positive) inthe range of ±90 degrees.

In this implementation, one packet has sufficient capacity for urgentinformation to be sent and the latest position information can beattached to the packet anytime. Furthermore, the vector from theemergency vehicle to the car, its starting position is not the positionof the emergency vehicle, but is an offset position (for example, about20 meters behind the back of the emergency vehicle) is applied.

Besides, relay terminal 2 can be controlled to relay packets, receivedfrom the emergency vehicle equipping information transmission source 1,to other vehicles providing relay terminal 3-n only when “cosine θ>α”.Here, α is a fixed real number. In other words, relay terminal 2 relayspackets only when its own vehicle is in the range among arccosine α. Forexample, relay terminal 2 relays packets to other vehicles among ±45degrees, in the direction the emergency vehicle moves, when α=1/{squareroot}2.

Also, the direction can be the direction to the final destination forthe emergency vehicle. It will be helpful for vehicles around theemergency vehicle, to avoid being disturbed every time the emergencyvehicle turns and to decide the range to broadcast packets.

Here, (1) is the formula expressing position vector of the car, (2) isthe formula expressing the speed vector of the car, (3) is the formulaexpressing the position vector, received from the emergency vehicle, (4)is the formula expressing the speed vector, received from the emergencyvehicle.{right arrow over (L)}₁=(x₁,y₁)  (1){right arrow over (V)}₁=(ν_(x1),ν_(y1))=(ν,sin θ₁, ν₁,cos θ₁)  (2){right arrow over (L)}₂=(x₂,y₂)  (3){right arrow over (V)}₂=(ν_(x2),ν_(y2))=(ν₂,sin θ₂,ν₂,cos θ₂)  (4)

Here, ν₁ is the speed of the car equipping relay terminal 2, θ₁ is thedirection of the movement of the car equipping relay terminal 2. ν₂ isthe movement speed of the emergency vehicle equipping informationtransmission source 1, and it makes θ₂ to the direction of the movementof the emergency vehicle equipping information transmission source 1.Also, γ[m] is coefficients of position offsets. Also, a judgment formulais the following formula (5). $\begin{matrix}{{\cos\quad\theta} = {\frac{\left\lbrack {{\overset{->}{L}}_{1} - {\overset{->}{L}}_{2} - {\gamma\quad\frac{{\overset{->}{V}}_{2}}{{\overset{->}{V}}_{2}}}} \right\rbrack \cdot {\overset{->}{V}}_{2}}{{{{\overset{->}{L}}_{1} - {\overset{->}{L}}_{2} - {\gamma\quad\frac{{\overset{->}{V}}_{2}}{{\overset{->}{V}}_{2}}}}}{{\overset{->}{V}}_{2}}} > \alpha}} & (5)\end{matrix}$

Here, “·” is the inner product and (χ1, y1)·(χ2, y2)=χ1χ2+y1y2.

FIG. 7 is the figure which explains the other implementation form ofthis invention. In this figure, an image of broadcasting the accidentinformation is shown. Hereinafter, process flow of this implementationis explained using the concrete examples such as broadcasting theaccident information. FIG. 4 is a flow chart showing the process flow.

In FIG. 4, the accident car, which is information transmission source 1,attaches “position information”, “position offset”, “relay terminalposition range”, “data available position range”, and “availabledirection” to the broadcast packet, and transmits them. Relay terminal2, providing in the car, receives the broadcast packet from informationtransmission source 1 via packet receiving part 21 (S21) and vectorcalculation part 23 gets the position vector, from the position of theinformation transmission source 1 to relay terminal 2, referring to itsown position information (S22). In this process, vector calculation part23 calculates above-mentioned position vector based on the positionwhich is shifted from the position of information from transmissionsource 1 just for the position offset. Then, vector calculation part 23calculates cosine θ from the inner product of the position vector andvector of the direction of its movement, and outputs cosine θ to bothrelay judgment part 24 and acceptance judgment part 25 (S23).

Relay judgment part 24 checks cosine θ (S24). When cosine θ is smallerthan a specific value β, for example 0, relay judgment part 24 takes thereceived packet as a candidate for relay and expects to extract datafrom the packet. Also, only when the received packet is the candidatefor relay, relay judgment part 24 checks the size of position vector(S25). When the size of position vector is smaller than “relay terminalposition range” of the received packet, relay judgment part 24 relaysthe packet (S26) and when the size of position vector is larger than“relay terminal position range”, relay judgment part 24 ignores thepacket (S29).

Also, acceptance judgment part 25 checks the size of the positionvector. When the size of the position vector is smaller than the “dataavailable position range”, acceptance judgment part 25 stores the data(S28). After that acceptance judgment part 25 requires applicationexecution part 27 to execute the appropriate application program.

Next, the implementation described above is explained to detail with aconcrete example of alerting information about a traffic accident.First, the accident car transmits the broadcasted packet (hereafter, anaccident information packet) including “position information” of theaccident car, “position offset”, “relay terminal position range”, “dataavailable position range”, “available angle (in this case, 90 degrees)”.

The car receives the accident information packet, and calculatesdistance from the accident car referring to the received packet. The carrelays the packet only when the distance from the accident car is lessthan the “relay terminal position range” and when the position vector of“the accident car to the car which received the packet” and directionvector of its movement turn to opposite ±90 degrees to each other (whenthe inner product is negative).

The car receives the broadcasted packet from the accident car andcalculates the position vector from the accident car to the carreferring to its own position information.

In this process, the car calculates the position vector based on theposition which was shifted (in order to stop the relay just a littleafter the car passes by the accident car) from the position of theaccident car just for the position offset (for example 20 meters behindthe accident car).

Similarly the car receives the packet and passes it to the applicationprogram when the distance from the accident car is less than “dataavailable position range” and when the position vector of the accidentcar to the car, received the packet, and direction vector turn toopposite ±90 degrees to each other (when the inner product is negative).

However, when the car detects “cosine θ<β”, it is also preferable tohave a rule of the packet receiving and sending process like that thecar relays only when the accident car is ahead of the car and in theangle range of arccosine β. For example, when β=1/{square root}2, thecar relays only in the case in which the accident car is in ±45 degreesahead of the car.

The judgment formula is shown in (6) below and the position of the caris shown in FIG. 8. $\begin{matrix}{{\cos\quad\theta} = {\frac{\left\lbrack {{\overset{->}{L}}_{1} - \overset{->}{L_{2}} - {\gamma\quad\frac{{\overset{->}{V}}_{1}}{{\overset{->}{V}}_{1}}}} \right\rbrack \cdot {\overset{->}{V}}_{1}}{{{{\overset{->}{L}}_{1} - {\overset{->}{L}}_{2} - {\gamma\quad\frac{{\overset{->}{V}}_{1}}{{\overset{->}{V}}_{1}}}}}{{\overset{->}{V}}_{1}}} < \beta}} & (6)\end{matrix}$

Here, “·” is the inner product and (χ1, y1)·(χ2, y2)=χ1χ2+y1y2.

Next, in another form of this invention, only when the car and theinformation transmission source car are facing each other, the carrelays or stores the packets from the information transmission sourcecar. FIG. 9 shows the situation including the car and the informationtransmission source car. The judgment formulas in this case are (7) andmoreover (8) below. $\begin{matrix}{{\cos\quad\theta_{1}} = {\frac{{\overset{->}{V}}_{2} \cdot {\overset{->}{V}}_{2}}{{{\overset{->}{V}}_{1}}{{\overset{->}{V}}_{2}}} < \beta_{1}}} & (7) \\{{\cos\quad\theta_{2}} = {\frac{\left\lbrack {{\overset{->}{L}}_{1} - {\overset{->}{L}}_{2} - {\gamma\quad\frac{{\overset{->}{V}}_{2}}{{\overset{->}{V}}_{2}}}} \right\rbrack \cdot {\overset{->}{V}}_{2}}{{{{\overset{->}{L}}_{1} - {\overset{->}{L}}_{2} - {\gamma\quad\frac{{\overset{->}{V}}_{2}}{{\overset{->}{V}}_{2}}}}}{{\overset{->}{V}}_{2}}} > \beta_{2}}} & (8)\end{matrix}$

Next, in another form of this invention, only when the car and theinformation transmission source car are going to be moving away fromeach other, the car relays or stores the packets from the informationtransmission source car. The judgment formulas in this case are (9) and(10) below. $\begin{matrix}{{\cos\quad\theta_{1}} = {\frac{{\overset{->}{V}}_{1} \cdot {\overset{->}{V}}_{2}}{{{\overset{->}{V}}_{1}}{{\overset{->}{V}}_{2}}} < \beta_{1}}} & (9) \\{{\cos\quad\theta_{2}} = {\frac{\left\lbrack {{\overset{->}{L}}_{1} - {\overset{->}{L}}_{2} - {\gamma\quad\frac{{\overset{->}{V}}_{2}}{{\overset{->}{V}}_{2}}}} \right\rbrack \cdot {\overset{->}{V}}_{2}}{{{{\overset{->}{L}}_{1} - {\overset{->}{L}}_{2} - {\gamma\quad\frac{{\overset{->}{V}}_{2}}{{\overset{->}{V}}_{2}}}}}{{\overset{->}{V}}_{2}}} > \beta_{2}}} & (10)\end{matrix}$

Next, in another form of this invention, only when the informationtransmission source car is on the right side or left side of the cardoes the car relay or store the packets from the informationtransmission source car. The judgment formulas in this case is (11)below. $\begin{matrix}{{\beta_{1} < {\cos\quad\theta}} = {\frac{\left( {{\overset{->}{L}}_{1} - {\overset{->}{L}}_{2}} \right) \cdot {\overset{->}{V}}_{2}}{{{{\overset{->}{L}}_{1} - {\overset{->}{L}}_{2}}}{{\overset{->}{V}}_{2}}} < \beta_{2}}} & (11)\end{matrix}$

From the explanation above, in this invention, a relay terminal checksand determines whether to relay the received broadcast packet toterminal that requires information, referring to the direction vectorand position information in the packet.

According to this invention, wireless terminals can avoid wasting theresources and each relay terminal can avoid sending packets which areunnecessary, so that terminals can avoid wasting electric power.

This invention is effective especially for broadcasting informationabout approaching emergency vehicle, broadcasting traffic accidentinformation in ITS and information distribution in an ad hock network.

Moreover, it is possible to construct a wireless network system andrelay terminal in this invention with a computer-readable storage mediumthat contains the processing steps of packet receiving part 21,self-position information acquisition part 22, vector calculation part23, relay judging part 24, acceptance judging part 25, data transmittingpart 26 and application execution part 27, and the computer that readsand executes the program.

The computer herein contains OS and hardware such as the peripheraldevices.

Also, when a “computer system” is connected to the WWW, this systemcontains home page provision environments (or display environments),too.

Also, the program, described above, can be transmitted from onecomputer, which stores the program in the storage and so on, to othercomputers via a transmission medium or transmission waves.

Here, a “transmission medium”, which transmits the program, is a mediumproviding the function to transmit information like the internet orother networks (communication networks), or telephone lines or othercommunications lines (telecommunication line).

Also, the program, described above, can provide some parts of the abovementioned functions.

Moreover, the program, described above, can realize the above mentionedfunctions together with the program already stored in the computer. Thistype of program can be a so-called difference file (difference program).

While preferred embodiments of the invention have been described andillustrated above, it should be understood that these are exemplary ofthe invention and are not to be considered as limiting. Additions,omissions, substitutions, and other modifications can be made withoutdeparting from the spirit or scope of the present invention.Accordingly, the invention is not to be considered as being limited bythe foregoing description, and is only limited by the scope of theappended claims.

1. A wireless network system relaying a broadcast signal in multiplestages and distributes data to terminals there around, comprising: atransmission source terminal which generates the broadcast-signal; andmultiple relay terminals which determine whether it is necessary torelay a broadcast packet according to a direction vector and a positioninformation specified by the information transmission source terminalreferring to the position information and its own direction.
 2. A relayterminal in a wireless network system which relays a broadcast-signal inmultiple stages and distributes data to terminals there around,comprising: a packet receiving part which receives a broadcast packetfrom an information transmission source terminal; a self-positioninformation acquisition part which determines its own position; and arelay judging part which determines whether it is necessary to relay thebroadcast packet according to a direction vector and positioninformation in the broadcast packet, specified by the informationtransmission source terminal.
 3. The relay terminal in accordance withclaim 2, wherein the relay judging part determines whether to relay thebroadcast packet according to an available angle range specified by theinformation transmission source terminal in the broadcast packet.
 4. Therelay terminal in accordance with claim 2, wherein said relay judgingpart determines whether to relay the broadcast packet according to relayposition range in the broadcast packet, specified by the informationtransmission source terminal.
 5. The relay terminal in accordance withclaim 2, further comprising: an acceptance judging part which determineswhether to accept the broadcasted packet according to a data availablerange in the broadcast packet, specified by the information transmissionsource terminal.
 6. A program for a relay terminal in a wireless networksystem which relays a broadcast signal in multiple stages anddistributes data to terminals there around, comprising: a packetreceiving process which receives a broadcast packet from a transmissionsource; a self-position information acquisition process which obtainsposition of the relay terminal; and a relay judging process whichdetermines whether to relay the broadcast packet according to adirection vector in the broadcast packet, specified by the informationtransmission source terminal, and position information.